1. Field of the Invention
Apparatus for treatment of stormwater runoff through volume-control-based detention and minimization of pollutant remobilization.
2. Description of the Related Art
This invention relates generally to liquid purification and separation and, more specifically, to an apparatus for separation of pollutants in urban stormwater runoff from the runoff water. This apparatus utilizes gravitational separation and tortuosity, resulting from a plurality of baffles both perpendicular to and oblique to the primary water flow direction, to trap substances less-dense and more-dense than water. This invention is differentiated from prior art by improved resistance to pollutant remobilization, resulting from an iterative experimental hydraulic design process. In addition, this invention provides a degree of retention through volume-control that exceeds that provided by existing gravitational, sub-surface, stormwater treatment systems.
Impacts of stormwater runoff on receiving environments have been documented extensively in engineering and scientific literature. Section 402 of the Federal Clean Water Act (CWA) regulates stormwater discharges through the National Pollutant Discharge Elimination System (NPDES). Treatment of stormwater runoff using best management practices (BMPs) is a typical requirement of state and local regulations, as well. In the 1990s, there has been growing interest in ‘ultra-urban/space limited’ BMP's, such as sand filters, water quality inlets, and, reservoir/vault type of structures. Space constraints, high property values, soil conditions, and the proximity of other building foundations often preclude the use of conventional, space-intensive stormwater BMP's such as detention ponds. For in-fill construction or redevelopment in built-up urban areas, where pollutant loads from urban runoff are usually the greatest, unconventional stormwater treatment technologies may be necessary.
Vault-type treatment technologies have been widely used for stormwater treatment in urban areas; however, the effectiveness of these devices for removal of suspended solids and oil and grease has been only marginal. A great weakness of these types of devices has been that large storm events tend to flush out the system, thereby releasing pollutants that were previously removed.
Prior art in the field of this invention of which the applicant is aware includes the following:                U.S. Pat. No. 4,127,488, Bell, J. A. et al., November 1978, Method and apparatus for separating solids from liquids.        U.S. Pat. No. 4,136,010, Pilie, R. J. et al., January 1979, Catch basin interceptor.        U.S. Pat. No. 4,328,101, Broden, C. V., May 1982, Device for separating particulate matter from a fluid.        U.S. Pat. No. 4,363,731, Filippi, R., December 1982, Device for regulating the flow of waste waters.        U.S. Pat. No. 4,383,922, Beard, H. J., May 1983, Waste water clarifier.        U.S. Pat. No. 4,983,295, Lamb, T. J. et al., January 1991, Separator.        U.S. Pat. No. 4,985,148, Monteith, J. G., January 1991, Improved separator tank construction.        U.S. Pat. No. 5,004,534, Buzzelli, V., April 1991, Catch basin.        U.S. Pat. No. 5,186,821, Murphy, D. T., February 1993, Wastewater treatment process with cooperating velocity equalization, aeration, and decanting means.        U.S. Pat. No. 5,342,144, McCarthy, E. J., August 1994, Stormwater control system.        U.S. Pat. No. 5,520,825, Rice, W. M., May 1996, Oil-water separator.        U.S. Pat. No. 5,536,409, Dunkers, K. R., July 1996, Water treatment system.        U.S. Pat. No. 5,637,233, Earrusso, P. J., June 1997, Method and apparatus for separating grease from water.        U.S. Pat. No. 5,679,258, Petersen, R. N., October 1997, Mixed immiscible liquids collection, separation, and disposal method and system.        U.S. Pat. No. 5,759,415, Adams, T., June 1998, Method and apparatus for separating floating and non-floating particulate from rainwater drainage.        U.S. Pat. No. 5,788,848, Blanche, P. et al., August 1998, Apparatus and methods for separating solids from flowing liquids or gases.        U.S. Pat. No. RE30,793, Dunkers, K. R., November 1981, Apparatus for water treatment.        
In addition to the patents listed above, a number of inventions in the general field of stormwater treatment methods and devices were discovered during the patent search. The inventions listed below have an element or elements similar to the invention disclosed herein; however, additional elements, details of elements, and/or applications of the inventions differ significantly from the forms and functions of the present invention. While the inventions listed below are intended to provide stormwater treatment, the principle of operation for many of these devices is filtration rather than sedimentation.                U.S. Pat. No. 4,298,471, Dunkers, K. R., November 1981, Apparatus for equalization of overflow water and urban runoff in receiving bodies of water.        U.S. Pat. No. 4,377,477, Dunkers, K. R., March 1983, Apparatus for equalization of overflow water and urban runoff in receiving bodies of water.        U.S. Pat. No. 4,664,795, Stegall, W. A. et al., May 1987, Two-stage waste water treatment system for single family residences and the like.        U.S. Pat. No. 4,747,962, Smissom, B., May 1988, Separation of components of a fluid mixture.        U.S. Pat. No. 4,865,751, Smissom, B., September 1989, Separation of components of a fluid mixture.        U.S. Pat. No. 5,080,137, Adams, T. R., January 1992, Vortex flow regulators for storm sewer catch basins.        U.S. Pat. No. 5,232,587, Hegemier, T. E. et al., August 1993, Stormwater inlet filters.        U.S. Pat. No. 5,322,629, Stewart, W. C., June 1994, Method and apparatus for treating stormwater.        U.S. Pat. No. 5,403,474, Emery, G. R., April 1995, Curb inlet gravel sediment filter.        U.S. Pat. No. 5,437,786, Horsley, S. W. et al., August 1995, Stormwater treatment system/apparatus.        U.S. Pat. No. 5,480,254, Autry, J. L. et al., January 1996, Storm drain box filter and method of use.        U.S. Pat. No. 5,549,817, Horsley, S. W. et al., August 1996, Stormwater treatment system/apparatus.        U.S. Pat. No. 5,702,593, Horsley, S. W. et al., December 1997, Stormwater treatment system/apparatus.        U.S. Pat. No. 5,707,527, Knutson, J. H. et al., January 1998, Apparatus and method for treating stormwater runoff.        U.S. Pat. No. 5,730,878, Rice, T., March 1998, Contaminated waste water treatment method and device.        U.S. Pat. No. 5,744,048, Stetler, C. C., April 1998, Clog resistant storm drain filter.        U.S. Pat. No. 5,770,057, Filion, G., June 1998, Overflow water screening apparatus.        U.S. Pat. No. 5,779,888, Bennett, P. J., July 1998, Filtering apparatus.        U.S. Pat. No. 5,810,510, Urriola, H., September 1998, Underground drainage system.        U.S. Pat. No. 5,840,180, Filion, G., November 1998, Water flow segregating unit with endless screw.        U.S. Pat. No. 5,890,838, Moore, Jr. Et al., April 1999, Stormwater dispensing system having multiple arches.        U.S. Pat. No. 5,972,216, Acernese, P. L. et al., October 1999, Portable multi-functional modular water filtration unit.        U.S. Pat. No. 5,985,157, Leckner, J. P. et al., November 1999, Filter device.        
Previous vault or box type treatment devices used in wastewater or stormwater treatment applications acted as “flow-through” systems. In these previous devices, incoming flows enter the device, take a given period of time based on baffles and size to flow through the device, and then exit the device. If flows were coming in continuously, they would enter and exit the device at the same flow rate. Previous devices have different systems within the vault to channel, divert, or reduce flow rates inside the vault in order to facilitate gravity separation. All of these devices are somewhat effective at settling out particles down to a certain size or specific gravity, but none of these devices are effective at removing the very small size range of particles that make up the majority of toxic pollutants in storm water runoff. These particles are typically in the 100-micron and smaller size range, and simply will not settle out of the water if there are horizontal flow velocities present.
Most currently available stormwater treatment devices are designed to reduce the concentrations of pollutants in stormwater by screen, filter or enhanced gravitational separation (i.e. swirl concentrators). However, such systems provide little or no detention capture volume to mitigate the runoff peaks for small or large runoff events. In other words, these systems function as flow-through devices, resulting in the lack of capture volume and overall poor treatment performance. Specifically, much of the settleable materials trapped or deposited during more numerous smaller runoff events are agitated and remobilized, and wash out of these devices when larger and more intense runoff events occur.
Properly sized and maintained wet detention ponds (retention ponds) provide some of the most effective stormwater treatment available. Because of site-specific limitations, however many desirable features of wet detention ponds are not utilized in real world conditions. Available surface area, possible thermal pollution, attractive nuisance liabilities, mosquitoes and long-term maintenance access and disposal are some of the difficulties that must be addressed with a surface pond.